The present invention relates generally to a machine for stringing rackets, such as tennis rackets and the like, and more particularly to apparatus useful on such a machine for pulling string to the desired tension.
Various devices have been developed over the years for stringing a racket at a selected tension. However, even with the aid of such devices, the stringing process has proven to be very time consuming. In many cases this is due to the less than efficient manner in which the string is tensioned.
One type of stringing device often used comprises a base, a vise on the base for holding the head of a racket in a fixed position lying in a generally horizontal plane, and tensioning apparatus on the base adjacent the vise for tensioning the string. This apparatus includes a cylindric drum mounted on the base for rotational movement about a generally horizontal axis, grippers on the drum for gripping a string on the racket, and a lever attached to the drum carrying a tensioning weight positioned on the lever according to the tension at which the racket is to be strung. To tension the string, the grippers are operated to grip the string and the lever is allowed to swing down under its own weight and that of the tensioning weight to rotate the drum and grippers thereon for tensioning the string. To ensure that the desired tension is attained, the lever must come to rest at a substantially horizontal position. If it drops below horizontal, indicating that the desired tension has not been reached, the string must be clamped at the racket to hold the tension, the lever raised, and the process repeated, which involves regripping the string and then guessing where to position the lever to start the second "pull" so that when the lever is dropped it stops at a horizontal position. This process is not only extremely time consuming, it may also result in damage to the string due to the repetitive clamping and unclamping of the string at the racket.
Reference may be made to U.S. Pat. Nos. 4,125,259, 3,988,022 and U.S. Pat. No. Des. 253,772 for a description of racket-stringing machines generally in the field of this invention.